The most probable cause is using incorrect e-mail addresses. To check them, go to MODERATION / Shop contact details / "e-mail addresses" section. If they are correct, report a ticket with a problem description to server administrators.

Yes. Start with deciding on what information you would like to send in e-mail and to whom. To select an adequate group of customers (e.g. customers with registered account but never bought anything, only wholesalers etc.) go to CUSTOMERS / Customer analysis (CRM). There you will find a list of available search options. After clicking on Search a list of customers will be displayed. Select the ones you want to send a newsletter to with checkboxes and click on Send newsletter. Another step is newsletter sending form - it allows to enter message contents, subject etc.

Hard bounce means that it is not possible to deliver a message to a particular email address and it will not be available in the future either. The most frequent cause of a hard bounce is a spelling mistake in the email address or deleting the account by a user.

If a newsletter has not been sent to all the recipients of the campaign, you can resume its mailing. In order to do it go to MARKETING > E-mail and SMS newsletters > Sent e-mail newsletters statistics and click on the name of a campaign. If there is no "Resume sending" button the newsletter has been sent successfully to all the recipients.